When multiple nerve cells or muscle cells depolarize simultaneously or sequentially, they generate a bio-potential that can be detected as an electrical signal by an externally positioned electrical circuit. External electrical circuits have long been used to measure such relatively small but measurable bio-potentials. The electroencephalogram (EEG) and Auditory Evoked Potential (AEP) are examples of signals used to monitor brain cell activity.
Electrode apparatus for recording bio-potentials, for example for EEG biofeedback applications, include a minimum of one pair of electrodes, and a third electrode as the ground electrode. The pair of electrodes, including an “active” electrode and an “indifferent” electrode, record one channel of EEG signal. The active electrode is typically located on the head near a brain area being monitored, the indifferent electrode is located on the head, on an ear, or on the mastoid bone behind an ear, and the ground electrode is typically placed on the forehead or on an ear, but can be placed almost anywhere. Additional recording channels can be added as desired by adding additional electrodes.
Known electrodes and related apparatus for recording bio-potentials such as EEG's are disposable electrodes such as, but not limited to, disposable self-adhesive individual electrodes, ear clip electrodes, disc electrodes, needle electrodes and saline-based electrodes. With all types of electrodes, a key factor in obtaining accurate and relatively noiseless bio-potential recordings is maintaining adequate contact between the electrode and the skin, because bio-potentials are typically relatively small, i.e. less than about 20 mV, and the recordings are highly susceptible to noise and artifacts.
While the methods of ensuring proper electrical contact between the electrode and the skin vary somewhat with the type of electrode being used, the skin usually must be prepared by cleaning with alcohol and abrading with an electrode preparation gel. The steps of cleaning and abrading may be repeated several times for ideal surface preparation. Skin contact is established using an ear clip electrode with a metal clip that fastens to the outer ear, a self-adhesive disc electrode that adheres directly to an area of skin, or with a disc electrode having a cup that is filled with an electrode paste. These types of electrodes are unsuitable for use in areas with much hair, such as on the scalp, and generally provide electrical contact that is not very robust or long lasting, which affects the quality and duration of recordings that can be obtained.
Needle-type electrodes generally provide better and more long-lasting contact, and can be used on the scalp, but involves tedious, uncomfortable and costly procedure to secure contact. To utilize a needle-type electrode, the hair must be parted to reveal skin, a colloidin-treated gauze layer secured over the electrode, electrode gel injected with a hypodermic needle through a hole in an electrode cup, and finally the skin abraded with the blunt end of the needle.
Headband-type and hat-style electrode connectors which completely encircle the head of a patient are known, in which electrodes such as those described above, are coupled to a hat, or to a headband made of an elastomeric material that fits around the crown of the head, holding cup or disc-type electrodes in place across the forehead of the subject. Headband-type electrode connectors are typically used for recording signals from the frontal areas of the brain, and are less useful for recording from other areas of the brain because of the relatively poor signal quality that results. In addition, headband connectors still require careful skin preparation.
Saline-based electrodes are also known, in which salt water is used to maintain the electrical connection between electrode and skin, instead of electrode gel. An electrode connector such as a headband or clip is required for securing the electrodes to the head, and skin preparation is still required. Further, to maintain the proper electrical contact, the electrode placements must be carefully monitored to ensure that the mechanical contact is maximized and that the electrodes stay sufficiently wetted with the saline-based solution.
Each of the above-described electrodes and electrode apparatus may be utilized to monitor and record bio-potentials. The bio-potentials may be continuous, representative of normal brain activity, or may be evoked in response to an external stimuli. External stimuli may be provided to any of the sensory systems of a human body, and may include auditory stimuli delivered to the ear of the patient by a suitable delivery mechanism. Conventionally, the delivery mechanism for the external stimuli is separate from the electrodes employed to measure the evoked response, requiring additional setup and handling.
Known electrode apparatus and connectors are therefore limited by being annoying or uncomfortable for the subject, especially when placed on the head. With the additionally requirement of setting up a stimuli delivery system, the task can quickly become unduly complicated and time consuming. The discomfort or apprehension associated with the setup is a particular problem for children, infants, and uncooperative subjects. Interference by an uncooperative subject with the placement and contact of head electrodes can render recordings of evoked brain potentials impossible to obtain or useless because of minimal or inadequate contact.
A need therefore exists for an electrode apparatus configured adapted to deliver stimuli for measuring evoked potentials which is simply and comfortably positioned on the subject, which maintains adequate skin contact for obtaining measurable recordings, and which is readily and inexpensively adapted for use with small children and infants.